This invention is directed to correlation displacement transducers. In particular, this invention is directed to a user interface apparatus for a correlation displacement transducer having a selectable detector area.
Various known measurement transducers may use images acquired by a sensor array, and correlation between such images, to determine deformations and/or displacements. For example, one class of such devices may be based on acquiring a speckle image generated by illuminating an optically rough surface with a light source. The light source may be a coherent light source, such as a laser-generating light source. After the optically rough surface is illuminated by the light source, the light scattered from the optically rough surface may be imaged onto an optical sensor. The optical sensor may be a charge-coupled device (CCD), a semiconductor image sensor array, such as a CMOS image sensor array, or the like.
Prior to displacing or deforming the optically rough surface, a first initial speckle image, sometimes called a reference image, may be captured and stored. Then, after displacing the optically rough surface, a second or subsequent speckle image, sometimes called a current image, may be captured and stored. Conventionally, as much of the first and second speckle images as possible are then correlated or compared on a pixel-by-pixel basis. In general, a plurality of comparisons are performed. In each comparison, the first and second speckle images may be offset, or “synthetically” spatially translated, as by shifting the images electronically, relative to each other. Between each comparison, the amount of offset, or synthetic spatial translation, may be increased by a known amount, such as one image element, or pixel, or an integer number of image elements or pixels.
In each correlation or comparison, the image value of a particular pixel in the reference image may be multiplied by, subtracted from, or otherwise mathematically used in a function with, the image value of the corresponding second image pixel, where the corresponding second image pixel is determined based on the amount of offset. The value resulting from each pixel-by-pixel operation may be accumulated with values resulting from the operation performed on every other pixel of the images to determine a correlation value for that comparison between the first and second images. That correlation value may then be, in effect, plotted against the offset amount, or synthetic spatial translation position, for that comparison, to determine a correlation function value point. The offset amount, or spatial translation position, having the strongest correlation between the reference and first images may generate an extremum, that is, a peak, or a trough, depending on how the pixel-by-pixel comparison is performed, in the plot of correlation function value points. The offset amount, or spatial translation position, corresponding to the peak or trough may represent the amount of relative displacement or deformation between the first and second speckle images.
Similarly, conventional images may be used in image correlation displacement sensing system systems. For such applications, the light source may be an incoherent source, such as a light emitting diode (LED), and the scale or surface to be imaged may be located at an object-side focal plane of imaging optics used to image a pattern of the scale or surface onto an optical sensor of a correlation displacement transducer.